Chapter 2.5（课件）- 《统计学基础（英文版）》同步教学（人民大学版）

Chapter Descriptive Statistics 2 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. 1 Larson/Farber 6th ed Chapter 1 Chapter Outline 2.1 Frequency Distributions and Their Graphs 2.2 More Graphs and Displays 2.3 Measures of Central Tendency 2.4 Measures of Variation 2.5 Measures of Position 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Section 2.5 Measures of Position . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Section 2.5 Objectives How to find the first, second, and third quartiles of a data set, how to find the interquartile range of a data set, and how to represent a data set graphically using a box-and whisker plot How to interpret other fractiles such as percentiles and how to find percentiles for a specific data entry Determine and interpret the standard score (z-score) . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Quartiles Fractiles are numbers that partition (divide) an ordered data set into equal parts. Quartiles approximately divide an ordered data set into four equal parts. First quartile, Q1: About one quarter of the data fall on or below Q1. Second quartile, Q2: About one half of the data fall on or below Q2 (median). Third quartile, Q3: About three quarters of the data fall on or below Q3. . 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Example: Finding Quartiles Each year in the U.S., automobile commuters waste fuel due to traffic congestion. The amounts (in gallons per year) of fuel wasted by commuters in the 15 largest U.S. urban areas are listed. Find the first, second, and third quartiles of the data set. What do you observe? (Source: Based on 2015 Urban Mobility Scorecard) 20 30 29 22 25 29 25 24 35 23 25 11 33 28 35 Solution: Q2 divides the data set into two halves. 11 20 22 23 24 25 25 25 28 29 29 30 33 35 35 . Data entries to the left of Q2 Data entries to the right of Q2 Q2 Q3 Q1 1 Copyright 2019, 2015, 2012, Pearson Education, Inc. Solution: Finding